One problem with the concave "vessel" design of watercraft is that excess watercraft volume is required above the water line to accommodate weight shift and to prevent catastrophic failure from water spilling into the vessel. That is, an open displacement vessel must have a large volume that increases from its bottom to top and that presents a vertical or concave shape, which creates a maximum of friction at the water surface. Such a concave hull efficiently transmits and receives energy to and from the water surface. The hull loses energy to the water and creates a wave (wake) simply by moving. The wake increasingly impedes boat movement as the boat acquires velocity, and becomes a standing wave at what is known as a limiting "hull-speed." Conversely a displacement vessel absorbs wave energy and is easily rocked by waves. Because of this sensitivity to waves a traditional "personal" watercraft that typically is less than 30 feet long, and particularly less than 25 feet long often cannot be used in the ocean when large waves are present. To overcome the large wave problem, a vessel type of watercraft simply is made larger. However, this solution is impractical for personal watercraft, especially trailorable watercraft that are limited in size by the dimensions of vehicles that can travel behind a car or truck on a highway.
The drawbacks of the traditional vessel displacement hull design are worsened when combined with electric propulsion systems. Boats that rely on rechargeable batteries, (which includes fuel cells in this context) have to carry a heavy and bulky power source. The great weight of the power source requires yet a larger hull to displace a larger volume of water to keep the boat afloat. This interferes with hull streamlining and can make the boat larger to accommodate the power source. Thus, the development of electric watercraft technology in particular is hindered by the vessel hull problem. In fact, the vessel hull drag prevents economical use of electric motors that utilize batteries for even moderate speed (above 8 mph) boating. This unfortunate state of affairs is a well known problem with electric boats, as, for example, stated in DOUGLAS LITTLE, ELECTRIC BOATS, THE QUIET HANDBOOK OF CLEAN, QUIET BOATING, (International Marine, 1994) on page 33 (referring to propeller design): "In the case of the electric boat, high speed-above 10 mph-is one factor that can be dropped immediately." Clearly, new designs are needed for wide acceptance of electric boats as general-purpose personal watercraft.
There is no comprehensive combination approach to this problem that plays off some disadvantage(s) of using heavy batteries or other low energy density power source with other disadvantage(s). In particular, no design strategy has successfully exploited the large mass and volume requirement of electric (including fuel cell) batteries as an asset, instead of a demerit, in a boat structure. Finally, there is no sufficient design for an electric powered and trailorable watercraft that can withstand moderate wave activity such as 2 feet high waves, without requiring a large vessel that cannot easily be pulled behind a car. A solution to these problems would open up new areas of boating to those that cannot buy or use the much greater size boats needed during moderate wave activity.